Techniques for selective activation of neurons in the brain, spinal cord parenchyma or peripheral nerve

ABSTRACT

The present invention discloses techniques capable of selectively affecting and adjusting a volume of neural tissue in the brain, parenchyma of the spinal cord, or a peripheral nerve. The invention preferably utilizes a lumen having at least one opening at its distal end that is capable of directing a lead outwardly along a predetermined trajectory. The lumen is capable of accepting a plurality of leads that can project outward in different directions from the distal end of the lumen. The leads have one or more electrodes at its ends and are thereby configured by the lumen in accordance with a predetermined two- or three-dimensional geometry. Anode/cathode relationships may be then established between the electrodes as desired by the operator to stimulate the neural tissue surrounding these electrodes. The operator may also adjust the stimulation to selectively stimulate the desired portion of the brain, spinal cord, peripheral nerve. In other embodiments, the present invention may be implemented to provide drug infusion. Sensor feedback may be implemented to adjust the treatment therapy.

[0001] This patent application is a continuation of U.S. patentapplication Ser. No. 09/302,519, filed Apr. 30, 1999, for which priorityis claimed. This parent application is incorporated herein by referencein its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present Invention relates to techniques for providingtreatment therapy to neural tissue, and more particularly relates totechniques for selectively delivering treatment therapy to neural tissuelocated within a volume of the brain, spinal cord, or peripheral nerve.

[0004] 2. Description of Related Art

[0005] Electrical stimulation techniques have become increasinglypopular for treatment of pain and various neurological disorders.Typically, an electrical lead having one or more electrodes is implantednear a specific site in the brain or spinal cord of a patient. The leadis coupled to a signal generator which delivers electrical energydelivered through the electrodes creates an electrical field causingexcitation of the nearby neurons directly or indirectly treat the painor neurological disorder.

[0006] Presently, only highly skilled and experiences practitioners areable to position a stimulation lead in such a way that the desiredvolume of brain tissue is influences and desired results are obtainedover time with minimal side effects. It requires much time and effort tofocus the stimulation on the population of nerve cells subserving theappropriate function in the desired body region during surgery. Theseleads cannt be moved by the physician without requiring a secondsurgery.

[0007] A major practical problem with these systems is that the responseof the nervous system may change in time. For example, when treatingpain even if paresthesia covers the area in pain perfectly duringsurgery, the required paresthesia pattern often changes later due tolead migration, histological changes (such as the growth of connectivetissue around the stimulation electrode), neural plasticity or diseaseprogression. As a result, the electrical energy is directed to stimulateundesired portions of the brain or spinal cord. Redirecting paresthesiawithout requiring a second surgery is therefore highly desirable. Withpresent single channel, linear electrode array approaches, however, itis difficult to redirect stimulation effects afterwards, even thoughlimited readjustments can be made by selecting a different contactcombination, pulse rate, pulse width or voltage. These problems arefound not only with spinal cord stimulation (SCS), but also withperipheral nerve stimulation (PNS), depth brain stimulation (DBS),cortical stimulation and also muscle or cardiac stimulation.

[0008] In the case of DBS where an electrical lead is implanted withinthe brain, it is particularly critical that the lead be properlypositioned. If the lead is not properly positioned and needs to bemoved, it must be removed and re-inserted thereby increasing the risk ofbleeding and damage to the neuropile. It is therefore desirable to placethe lead within the brain in one attempt and avoid subsequent movementor repositioning of the lead.

[0009] Recent advances in this technology have allowed the treatingphysician or the patient to steer the electrical energy delivered by theelectrode once it has been implanted within the patient. For example,U.S. Pat. No. 5,713,922 entitled “Techniques for Adjusting the Locus ofExcitation of Neural Tissue in the Spinal Cord or Brain,” issued on Feb.3, 1998 to and assigned to Medtronic, Inc. discloses one such example ofa system for steering electrical energy. Other techniques are disclosedin application Ser. No. 08/814,432 (filed Mar. 10, 1997) and Ser. No.09/024,162 (filed Feb. 17, 1998). Changing the electric fielddistribution changes the distribution of neurons recruited during astimulus output thus provides the treating physician or the patient theopportunity to alter the physiological response to the stimulation. Thesteerability of the electric field allows the user to selectivelyactivate different groups of nerve cells without physically moving theelectrode.

[0010] These steering techniques, however, are limited to primarilytwo-dimensional steering since the electrodes are positioned in a linearor planar configuration. In the case of deep brain stimulation (DBS),the stimulation treatment requires stimulation of a volume of neuraltissue. Since the exact location of the desired tissue is unknown, it isdesirable to steer the electrical field in more than justtwo-dimensional space.

[0011] Another problem with DBS is that the insertion of electricalleads within the brain presents risks of bleeding or damage to the braintissue. Where multiple leads are inserted within the brain, this riskalso multiplies. Often during placement of a lead within the brain, thelead is not placed in the desired location. The lead must be removed andre-inserted into the brain. Each re-insertion of the lead posesadditional risk of injury.

[0012] Accordingly, there remains a need in the art to provide a two- orthree-dimensional steerable electrical stimulation device that may beimplanted within the brain or spinal cord parenchyma that requiresminimal adjustment of the lead position.

SUMMARY OF THE INVENTION

[0013] As explained in more detail below, the present inventionovercomes the above-noted and other shortcomings of prior techniques forelectrical stimulation of the brain, spinal cord parenchyma andperipheral nerve. The present invention provides a technique forinsertion of electrode leads that require minimal adjustment once thelead has been inserted. Additionally, the present invention enables theuser to selectively stimulate neurons or neural tissue within a specificvolume of tissue. In a preferred embodiment, the present inventionincludes a cannula, a plurality of leads, and at least one therapydelivery element or electrode at the distal ends of each of the leads.The cannula has a lumen and at least two openings at its distal end. Theleads may be inserted into the cannula's lumen and projected outward atthe distal end from each of the openings along a predeterminedtrajectory. A therapy delivery device, such as a signal generator, iscoupled to one or more therapy delivery elements, such as electrodes.The signal generator is capable of selectively providing electricalenergy via the electrode to create an electrical field. The system mayselectively adjust the electrical field created by the electricalenergy. Optionally, a sensor may be included for generating a signalrelated to the extent of a physical condition for treating aneurological disorder or pain. The sensor signal may then be used toadjust at least one parameter of the electrical energy provided to theelectrode.

[0014] In another embodiment, the present invention is implementedwithin a drug delivery system. In such a case, the therapy deliverydevice may be a pump and the therapy delivery element is a catheter.Alternatively, both electrical stimulation and drug delivery may beimplemented.

[0015] By using the foregoing techniques, electrical stimulation and/ordrug delivery may be adjusted and/or steered to a precise target withina volume of neural tissue to provide the desired treatment therapy.Further, the present invention provides a method of lead placement thatallows the surgeon to explore a larger volume of brain tissue using onlya single pass of the lead introducer into the brain which will reducethe inherent risk of surgery. Examples of the more important features ofthis invention have been broadly outlined above so that the detaileddescription that follows may be better understood and so thatcontributions which this invention provides to the art may be betterappreciated. There are, of course, additional features of the inventionwhich will be described herein and which will be included within thesubject matter of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] These and other advantages and features of the invention willbecome apparent upon reading the following detailed description andreferring to the accompanying drawings in which like numbers refer tolike parts throughout and in which:

[0017]FIG. 1 is a schematic view of a patient having an implant of aneurological stimulation system employing a preferred form of thepresent invention to stimulate the subthalamic nucleus of the patient;

[0018]FIG. 2 is a cross sectional view of brain B showing implantationof a cannula within the brain;

[0019]FIG. 3 is a sagittal view of a subthalamic nucleus showingimplantation of electrical leads having electrodes at the distal ends;

[0020] FIGS. 4-7 are exemplary illustrations of various electrical leadconfigurations capable of selectively stimulating a volume of neuraltissue in accordance with the present invention;

[0021]FIG. 8 is an illustration of a cannula in accordance with apreferred embodiment of the present invention;

[0022]FIGS. 9 and 9A are cross sectional views of a cannula inaccordance with another embodiment of the invention;

[0023]FIG. 10 is an illustration of a guiding mechanism to be insertedwithin a cannula for directing the trajectory of the electrical leads ofthe present invention;

[0024]FIG. 11 is an illustration of another embodiment of the presentinvention wherein one or more drugs are delivered;

[0025] FIGS. 12A-B illustrate another embodiment of the presentinvention wherein the outer leads are pre-formed so that the distal endswill curl out from the inner lead when unconstrained by an introducingcannula;

[0026]FIG. 13 is a schematic block diagram of a microprocessor andrelated circuitry used in the preferred embodiment of the invention;

[0027] FIGS. 14-18 are flow charts illustrating a preferred form of amicroprocessor program for generating stimulation pulses to beadministered to the brain;

[0028]FIG. 19 is a schematic block diagram of a sensor and analog todigital converter circuit used in the preferred embodiment of theinvention;

[0029]FIG. 20 is a flow chart illustrating a preferred form of amicroprocessor program for utilizing the sensor to control the treatmenttherapy of the brain;

[0030]FIG. 21 is a cross-sectional view of the present inventionimplanted subdurally within the cerebral spinal fluid;

[0031]FIG. 22 is a cross-sectional view of the present inventionimplanted subdurally within spinal cord parenchyma; and

[0032]FIG. 23 is a cross-sectional view of the present inventionimplanted within a peripheral nerve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033]FIG. 1 is a schematic view of a patient 10 having an implant of aneurological stimulation system employing a preferred form of thepresent invention to stimulate the subthalamic nucleus of the patient.The preferred system employs an implantable therapy delivery device or apulse generator 14 to produce a number of independent stimulation pulseswhich are sent to a region of the brain parenchyma such as thesubthalamic nucleus by insulated leads coupled to therapy deliverydevices or electrodes 16A-18A (FIG. 3). Each lead is inserted withincannula 22A. Alternatively, two or more electrodes 16A-18A may beattached to separate conductors included within a single lead. FIG. 2 isa cross section of brain B showing implantation of cannula 22A withinthe brain. The specific locations within the brain are discussed infurther detail herein.

[0034] Device 14 is implanted in a human body 120 in the location shownin FIG. 1. Body 120 includes arms 122 and 123. Alternatively, device 14may be implanted in the abdomen or any other part of the body.

[0035] Implantable pulse generator 14 is preferably a modifiedimplantable pulse generator available from Medtronic, Inc. under thetrademark ITREL II with provisions for multiple pulses occurring eithersimultaneously or with one pulse shifted in time with respect to theother, and having independently varying amplitudes and pulse widths.This preferred system employs a programmer 20 which is coupled via aconductor 31 to a telemetry antenna 24. The system permits attendingmedical personnel to select the various pulse output options afterimplant using telemetry communications. While the preferred systememploys fully implanted elements, systems employing partially implantedgenerators and radio-frequency coupling may also be used in the practiceof the present invention (e.g., similar to products sold by Medtronic,Inc. under the trademarks X-trel and Mattrix).

[0036]FIG. 3 is a sagittal view of the subthalamic nucleus 10 of brain Bat approximately 11 mm lateral to the midline. The distal ends ofinsulated leads 16-18 within cannula 22A terminate in electrodes16A-18A. The electrodes may be conventional DBS™ electrodes, such asmodel 3387 sold by Medtronic, Inc. Alternatively, electrodes 16A-18A maybe constructed like electrical contacts 56, 58 and 60 shown in PCTInternational Publication No. WO 95/19804, entitled “MultichannelApparatus for Epidural Spinal Cord Stimulation” (Holsheimer et al.,filed Jan. 24, 1994, published Jul. 27, 1995) which is incorporated byreference in its entirety. Electrodes 16A-18A are positioned in a two-or three-dimensional predetermined geometric configuration as describedin further detail herein such that they are distributed throughoutvarious portions of a volume of brain parenchyma such as the subthalamicnucleus. An anode/cathode relationship is established between electrodes16A-18A in the manner described in PCT Publication No. WO 95/19804. Forexample, electrodes 16A and 18A may be established as anodes (+) andelectrode 17A may be established as a cathode (−). The physician orpatient may configure the system to utilize any combination ofelectrodes 16A-18A to selectively establish a locus of actionpotentials.

[0037] Pulses may then be applied to specific electrodes as taught inthe PCT Publication No. WO 95/19804 to direct a locus of actionpotentials in the brain. Pulses in electrodes 16A-18A create a locus ofexcitation of nerve cells. As preferred, the electrical pulses areindependently adjustable within each electrode such that the locus ofexcitation may be adjusted to deliver the desired therapy. For example,the pulses may overlap in time and may be independently variable inamplitude to best control the areas of activation, or they may also haveindependently variable pulse widths.

[0038] In accordance with the present invention, a volume of neuraltissue may be stimulated by placement of electrical leads in anon-linear configuration. FIGS. 4-7 illustrate various electrical leadconfigurations capable of selectively stimulating a volume of neuraltissue. Lead 400 of FIG. 4 includes six electrodes at its distal enddefining the sides of a cube 405 as shown in FIG. 4A. Cube 405 roughlyrepresents the volume of brain parenchyma that electrodes maypotentially stimulate. The subset of tissue actually stimulated isdetermined by the selection of the particular electrodes to pulse andthe pulsing parameters. Lead 400 is preferably five separate leadsbundled together. The center lead 401 may be advanced beyond the distalends of the four outer leads 402 forming the outer surface of cube 405.In this embodiment, the inner lead may also be extended a variabledistance from the distal tip of the outer tube. As an example, lead 400of FIG. 5 shows the situation when five (5) electrodes at its distal endare positioned in a planar configuration as shown in FIG. 5A. This isaccomplished by advancing inner lead 401 only as far as needed toposition the most distal electrode in the same plane as those curledleads. As illustrated in FIGS. 6, 6A, 7 and 7A those skilled in the artwill appreciate that any number of lead and electrode configurations maybe possible and still be considered within the spirit and scope of thepresent invention. For example, another electrode may be on inner lead401 and positioned right at the point where leads split apart. The leadof the present invention may also provide for drug delivery as shown inFIG. 11 and discussed herein.

[0039] Each electrode may be individually connected to signal generator14 through a conductor in cables 22 which is coupled to signal generator14 in the manner shown in FIG. 1. Alternatively, each electrode may becoupled to signal generator 14 in a manner disclosed in application Ser.No. 09/024,162 entitled “Living Tissue Stimulation and RecordingTechniques with Local Control of Active Sites” and filed Feb. 17, 1998.The electrodes of FIGS. 4-7 may be selectively powered as an anode,cathode or neither. The operator or patient preferably may alsoselectively adjust the energy, amplitude or pulse parameters deliveredto each electrode. The selective control over each electrode may beachieved by signal generator 14 via programmer 20 or a separatecontroller such as that disclosed in application Ser. No. 09/024,162.Advantageously, the present invention allows the locus of excitation tobe selectively adjusted and/or steered to precisely target portions ofthe brain to achieve the desired treatment therapy. The steering may beaccomplished in the manner described in U.S. Pat. No. 5,713,922 which isincorporated herein by reference in its entirety.

[0040]FIG. 8 is an illustration of an alternative embodiment of a threedimensional electrode array having a lumen 800 for directing thetrajectory of the electrical leads of the present invention. Lumen 800is permanently introduced into the brain parenchyma to a region roughlyin the center of the volume of brain the user wishes to influence. Lumen800 has a proximal end 805 for accepting one or more leads 815A-818A anda distal end 810 having openings 815-818 for directing leads 815A-818Ain accordance with a desired trajectory. Ends of leads 815A-818A mayprotrude from openings 815-818 as needed to achieve the desiredgeometric configuration. It is preferred that leads 815A-818A protrudeout from openings 815-818 along a predetermined trajectory.Advantageously, the present invention avoids any slicing movement ofleads 815A-818A while moving outwardly from the central axis of lumen800 thereby minimizing any risks of damage or bleeding to the braintissue. Optionally, leads 815A-818A may be made of a silicon materialhaving a predetermined bend or memory along its body to ensure thatleads 815A-818A project from an opening at the desired angle.

[0041] Openings 815-818 preferably direct leads 815A-818A along apredetermined angle and trajectory. FIG. 9 shows a cross-sectional viewof cannula 905 along its distal end showing the two openings. FIG. 9Aillustrates a lead 920 as it is positioned within cannula 905 and leadend 910 is guided out from cannula 905 by opening 915. FIG. 10illustrates the interior portion 905 of a cannula capable of receivingfour leads. Interior portion may be inserted within a standard cannula.Those skilled in the art will appreciate that any number ofconfigurations are possible to achieve the desired geometricconfigurations of the electrodes. Additionally, lead members may containmore than one electrode near their distal end further expanding thegeometric options for selectively activating subsections of brainvolume.

[0042] The present invention is implanted by first implanting cannula800 so that its distal end 810 is at a predetermined location within thebrain. Each lead is then individually inserted within cannula 800 andpositioned such that the electrode is at the desired location within thebrain.

[0043]FIG. 12 illustrates another embodiment of the present inventionwherein four outer leads 450 are pre-formed so that the distal ends willcurl out from the inner lead 465 when unconstrained by an introducingcannula 460. Outer leads 450 and inner lead 465 may be a single leadstructure. Cannula 460 may be a standard cannula of a sufficiently largelumen to accept a plurality of leads. Cannula 460 may also be utilizedto implant the leads of FIGS. 4-7. Referring back to FIG. 12, lead 450may be given a predetermined curvature or memory so that the four outerleads 450 curl out when no longer constrained by the inner wall ofcannula 460 as shown in FIG. 12A. Again, the outer leads 450 preferablyextend out into the brain parenchyma along a predetermined trajectory tominimize injury to brain tissue.

[0044] Optionally, the present invention may incorporate a closed-loopfeedback system to provide automatic adjustment of the electricalstimulation therapy. The system may incorporate a sensor 130 to providefeedback to provide enhanced results. Sensor 130 can be used with aclosed loop feedback system in order to automatically determine thelevel of electrical stimulation necessary to provide the desiredtreatment. Sensor 130 may be implanted into a portion of a patient'sbody suitable for detecting symptoms of the disorder being treated.Sensor 130 is adapted to sense an attribute of the symptom to becontrolled or an important related symptom. Sensors suitable for thispurpose may include, for example, those disclosed in U.S. Pat. No.5,711,316 entitled “Method Of Treating Movement Disorders By BrainInfusion” assigned to Medtronic, Inc., which is incorporated herein byreference in its entirety. In cases where the attribute of the symptomis the electrical activity of the brain, stimulating electrodes may beintermittently used to record electrical activity.

[0045] As shown in FIG. 19, the output of sensor 130 is coupled by acable 132 comprising conductors 134 and 135 to the input of analog todigital converter 206. Alternatively the output of the sensor 130 couldcommunicate through a “body bus” communication system as described inU.S. Pat. No. 5,113,859 (Funke), assigned to Medtronic which isincorporated by reference in its entirety. Alternatively, the output ofan external feedback sensor 130 would communicate with the implantedpulse generator 14 or pump 10A through a telemetry down-link. The outputof the analog to digital converter 206 is connected to terminals EF2 BARand EF3 BAR. Such a configuration may be one similar to that shown inU.S. Pat. No. 4,692,147 (“'147 patent”) except that before converter 206is connected to the terminals, the demodulator of the '147 patent(identified by 101) would be disconnected.

[0046] Alternatively, one or more electrodes implanted within the brainmay serve as a sensor or a recording electrode. When necessary thesesensing or recording electrodes may delivery stimulation therapy to thetreatment site.

[0047] For some types of sensors, a microprocessor and analog to digitalconverter will not be necessary. The output from sensor 130 can befiltered by an appropriate electronic filter in order to provide acontrol signal for signal generator 14. An example of such a filter isfound in U.S. Pat. No. 5,259,387 “Muscle Artifact Filter, Issued toVictor de Pinto on Nov. 9, 1993, incorporated herein by reference in itsentirety.

[0048] Closed-loop electrical stimulation can be achieved by a modifiedform of the ITREL II signal generator which is described in FIG. 13. Theoutput of the analog to digital converter 206 is connected to amicroprocessor 200 through a peripheral bus 202 including address, dataand control lines. Microprocessor 200 processes the sensor data indifferent ways depending on the type of transducer in use. When thesignal on sensor 130 exceeds a level programmed by the clinician andstored in a memory 204, increasing amounts of stimulation will beapplied through an output driver 224.

[0049] The stimulus pulse frequency is controlled by programming a valueto a programmable frequency generator 208 using bus 202. Theprogrammable frequency generator provides an interrupt signal tomicroprocessor 200 through an interrupt line 210 when each stimuluspulse is to be generated. The frequency generator may be implemented bymodel CDP1878 sold by Harris Corporation. The amplitude for eachstimulus pulse is programmed to a digital to analog converter 218 usingbus 202. The analog output is conveyed through a conductor 220 to anoutput driver circuit 224 to control stimulus amplitude. Microprocessor200 also programs a pulse width control module 214 using bus 202. Thepulse width control provides an enabling pulse of duration equal to thepulse width via a conductor . Pulses with the selected characteristicsare then delivered from signal generator 14 through cable 22 and lead22A to the target locations of a brain B. Microprocessor 200 executes analgorithm to provide stimulation with closed loop feedback control asshown in U.S. Pat. No. 5,792,186 entitled “Method and Apparatus ofTreating Neurodegenerative Disorders by Electrical Brain Stimulation,”and assigned to Medtronic, Inc., which is incorporated herein byreference in its entirety.

[0050] Microprocessor 200 executes an algorithm shown in FIGS. 14-18 inorder to provide stimulation with closed loop feedback control. At thetime the stimulation device 14 is implanted, the clinician programscertain key parameters into the memory of the implanted device viatelemetry. These parameters may be updated subsequently as needed. Step400 in FIG. 14 indicates the process of first choosing whether theneural activity at the stimulation site is to be blocked or facilitated(step 400(1)) and whether the sensor location is one for which anincrease in the neural activity at that location is equivalent to anincrease in neural activity at the stimulation target or vice versa(step 400(2)). Next the clinician must program the range of values forpulse width (step 400(3)), amplitude (step 400(4)) and frequency (step400(5)) which device 14 may use to optimize the therapy. The clinicianmay also choose the order in which the parameter changes are made (step400(6)). Alternatively, the clinician may elect to use default values.

[0051] The algorithm for selecting parameters is different depending onwhether the clinician has chosen to block the neural activity at thestimulation target or facilitate the neural activity. FIG. 14 detailssteps of the algorithm to make parameter changes.

[0052] The algorithm uses the clinician programmed indication of whetherthe neurons at the particular location of the stimulating electrode areto be facilitated or blocked in order to reduce the neural activity inthe target nucleus to decide which path of the parameter selectionalgorithm to follow (step 420, FIG. 15). If the neuronal activity is tobe blocked, device 14 first reads the feedback sensor 130 in step 421.If the sensor values indicate the activity in the target neurons is toohigh (step 422), the algorithm in this embodiment first increases thefrequency of stimulation in step 424 provided this increase does notexceed the preset maximum value set by the physician. Step 423 checksfor this condition. If the frequency parameter is not at the maximum,the algorithm returns to step 421 through path 421A to monitor the feedback signal from sensor 130. If the frequency parameter is at themaximum, the algorithm next increases the pulse width in step 426 (FIG.16), again with the restriction that this parameter has not exceeded themaximum value as checked for in step 425 through path 423A. Not havingreached maximum pulse width, the algorithm returns to step 421 tomonitor the feedback signal from sensor 130. Should the maximum pulsewidth have been reached, the algorithm next increases amplitude in alike manner as shown in steps 427 and 428. In the event that allparameters reach the maximum, a notification message is set in step 429to be sent by telemetry to the clinician indicating that device 14 isunable to reduce neural activity to the desired level.

[0053] If, on the other hand, the stimulation electrode is placed in alocation which the clinician would like to activate in order to increasean inhibition of the target nucleus, the algorithm would follow adifferent sequence of events. In the preferred embodiment, the frequencyparameter would be fixed at a value chosen by the clinician tofacilitate neuronal activity in step 430 (FIG. 17) through path 420A. Insteps 431 and 432 the algorithm uses the values of the feedback sensorto determine if neuronal activity is being adequately controlled. Inthis case, inadequate control indicates that the neuronal activity ofthe stimulation target is too low. Neuronal activity is increased byfirst increasing stimulation amplitude (step 434) provided it doesn'texceed the programmed maximum value checked for in step 433. Whenmaximum amplitude is reached, the algorithm increases pulse width to itsmaximum value in steps 435 and 436 (FIG. 18). A lack of adequatereduction of neuronal activity in the target nucleus, even thoughmaximum parameters are used, is indicated to the clinician in step 437.After steps 434, 436 and 437, the algorithm returns to step 431 throughpath 431A, and the feedback sensor again is read.

[0054] It is desirable to reduce parameter values to the minimum levelneeded to establish the appropriate level of neuronal activity in thetarget nucleus. Superimposed on the algorithm just described is anadditional algorithm to readjust all the parameter levels downward asfar as possible. In FIG. 14, steps 410 through 415 constitute the methodto do this. When parameters are changed, a timer is reset in step 415.If there is no need to change any stimulus parameters before the timerhas counted out, then it may be possible due to changes in neuronalactivity to reduce the parameter values and still maintain appropriatelevels of neuronal activity in the target neurons. At the end of theprogrammed time interval, device 14 tries reducing a parameter in step413 to determine if control is maintained. If it is, the variousparameter values will be ratcheted down until such time as the sensorvalues again indicate a need to increase them. While the algorithms inFIG. 14 follow the order of parameter selection indicated, othersequences may be programmed by the clinician.

[0055] The features and advantages of the present invention for steeringan electric field within a brain, a spinal cord, or a peripheral nervemay be implemented in numerous applications. It is generally desirableto excite particular neural tissue elements of the brain to provide acertain treatment such as treatment of a neurological disorder, therelief of chronic pain or to control movements. Often, nearby groups ofneurons or axons, e.g., the optic nerve, internal capsule, or mediallemniscus, are in special orientations and groupings. It may beadvantageous to avoid affecting them (e.g., preventing stimulation ofthe perception of the flashes of light) or deliberately to affect them(e.g., excite or inhibit axons of passage). Advantageously, the presentinvention allows steering of the electrical filed in two- orthree-dimensional space such that the precise location and orientationof the electrodes is less critical.

[0056] Closed-loop feedback control may also be implemented to steer theelectric field to more precisely affect the desired treatment vollume ofneural tissue.

[0057] Referring back to FIG. 11, the present invention may also beimplemented within a drug delivery system. In this embodiment, thetherapy delivery device is a pump 10A and the therapy delivery elementis a catheter 23. A therapy delivery device or pump 10A made inaccordance with the preferred embodiment may be implanted below the skinof a patient. The device has a port 27 into which a hypodermic needlecan be inserted through the skin to inject a quantity of a liquid agent,such as a medication or drug. The liquid agent is delivered from pump10A through a catheter port 20A into a therapy delivery element or acatheter 23. Catheter 23 is positioned to deliver the agent to specificinfusion sites in a brain (B). Pump 10A may take the form of the devicenumbered 10 that is shown in U.S. Pat. No. 4,692,147 (Duggan), assignedto Medtronic, Inc., Minneapolis, Minn., which is incorporated byreference in its entirety.

[0058] The distal end of catheter 23 terminates in a cylindrical hollowtube 23A having a distal end 115 implanted into a portion of the brain Bby conventional stereotactic surgical techniques. Tube 23A is surgicallyimplanted through a hole in the skull 123. Catheter 23 is joined to pump10A in the manner shown.

[0059] The present invention may be used to deliver treatment therapy toany number of sites in the brain. Particular sites within the braininclude, for example, the subthalamic nucleus (STN), the peduncularpontine nucleus (PPN), the caudate or putamen, the internal and externalpallidum, the cingulum, the anterior limb of the internal capsule, theanterior nucleus (AN), the centremedian (CM), the dorsal medial nucleusand other nuclei of the thalamus, the hippocampus and other structuresin the temporal lobe, the hypothalamus and other structures of thediencephalon, the pons, the medulla, the corext, the cerebellum, thelateral geniculate body, and the medial geniculate body. The desiredconfiguration of the electrodes would depend upon the structure of theportion of the brain to be stimulated or infused and the angle ofintroduction of the deep brain cannula.

[0060] Further, lamina for visual fields are found in the lateralgeniculate body, and lamina for tones for hearing are found in themedial geniculate body. Hence, steering of excitation or inhibition byuse of this invention can be most useful.

[0061] Leads of the present invention may also be placed into theparenchyma of the spinal cord. For example, an electrode array may belocated in the region of a specified spinal cord segment where neuraltissue related to the bladder may be influenced. Selective activation ofregions of the ventral horn of the spinal cord in these spinal segmentsmay enable selective activation of specific actions related to bladderfunction. Alternatively, placement of leads in the region of the connusmedullaris (FIG. 22) or cauda equina (FIG. 21) may further enhance theability to selectively activate element of urinary bladder control.Leads 975 or 980 of FIGS. 21 or 22 may be implanted under knowntechniques for implanting leads within the spinal cord.

[0062] As shown in FIG. 23, leads of the present invention may also beplaced in a peripheral nerve to provide selective activation ofindividual nerve fascicles or neurons each innervating a different bodyregion or subserving a different physiological function. Selectiveactivation individual nerve fascicles or neurons may allowdiscrimination of regions of body surface when evoking paresthesiaactivation to treat chronic pain. Alternatively, such an embodimentwould allow selective activation of different muscle groups whenperforming functional electrical stimulation.

[0063] Advantageously, the present invention may be used to selectivelysteer and control the stimulation of neurons or neural tissue to delivera desired treatment therapy. Those skilled in that art will recognizethat the preferred embodiments may be altered or amended withoutdeparting from the true spirit and scope of the invention, as defined inthe accompanying claims. For example, the present invention may also beimplemented within a drug delivery system where the leads are implantedwithin the brain in accordance with the present invention to provideelectrical stimulation as well as delivery of one or more drugs.

We claim:
 1. A cannula for use with a therapy delivery device forproviding treatment therapy to a volume of neural tissue, the cannulacomprising in combination: (a) a proximal end capable of receiving atleast two leads; (b) a body; and (c) a distal end having at least twoapertures, each aperture capable of directing at least one of the leadsoutwardly along a distinct predetermined trajectory.
 2. A lead systemfor providing treatment therapy to a volume of neural tissue comprisingin combination: (a) cannula having a lumen distal end, the lumen distalend having at least two openings, each opening capable of directing alead outwardly along a distinct predetermined trajectory; (b) at leasttwo leads insertable within the cannula; and (c) at least one therapydelivery element at a distal end of each lead.
 3. The lead system ofclaim 2, wherein the therapy delivery element is an electrode to providestimulation therapy.
 4. The lead system of claim 2, further comprising:(d) a therapy delivery device selectively providing treatment therapyvia the therapy delivery element.
 5. The lead system of claim 4, whereinthe therapy delivery device is a signal generator and the therapydelivery element is an electrode.
 6. The lead system of claim 5, furthercomprising: (e) means for selectively adjusting an electric fieldcreated by delivery of stimulation energy to each electrode by thesignal generator.
 7. The lead system of claim 2, wherein the therapydelivery element is an catheter to delivery at least one therapeuticsubstance.
 8. The lead system of claim 4, wherein the therapy deliverydevice is a drug delivery device and the therapy delivery element is acatheter.
 9. The lead system of claim 8, further comprising: (e) meansfor selectively adjusting a relative drug delivery by the pump to eachcatheter.
 10. The lead system of claim 2, further comprising: (d) asensor for generating a signal related to an extent of a condition to betreated; and (e) a processor responsive to the sensor for adjusting atleast one parameter of a treatment therapy provided to the therapydelivery element.
 11. The lead system of claim 2, further comprising:(d) a sensor for generating a signal related to an extent of a conditionto be treated; and (e) a processor responsive to the sensor forselectively altering a relative treatment therapy delivery deliveredthrough the therapy delivery elements.
 12. A method for implanting leadsto provide treatment therapy to a volume of neural tissue comprising thesteps of: (a) positioning a cannula within a body of a patient, thecannula having at least two openings near a distal end, each openingcapable of directing a lead outwardly along a distinct predeterminedtrajectory; (b) inserting at least two leads into the cannula; and (c)directing a distal end of each lead outwardly through one of theopenings and along the distinct predetermined trajectory determined bythe opening.
 13. The method of claim 12, wherein the step of positioningcomprises the step of positioning the cannula within a brain of thepatient.
 14. The method of claim 12, wherein the step of positioningcomprises the step of positioning the cannula within a spinal cord ofthe patient.
 15. The method of claim 12, wherein the step of positioningcomprises the step of positioning the cannula within a peripheral nerveof the patient.
 16. A method for implanting leads to provide treatmenttherapy to a volume of neural tissue comprising the steps of: (a)implanting a cannula within a body of a patient; (b) inserting first andsecond leads into the cannula; (c) directing a first distal end of thefirst lead outwardly through the cannula and along a first distinctpredetermined trajectory; and (d) directing a second distal end of thesecond lead outwardly through the cannula and along a second distinctpredetermined trajectory.
 17. The method of claim 16, wherein the stepof implanting comprises the step of positioning the cannula within abrain of the patient.
 18. The method of claim 16, wherein the step ofimplanting comprises the step of positioning the cannula within a spinalcord of the patient.
 19. The method of claim 16, wherein the step ofimplanting comprises the step of positioning the cannula within aperipheral nerve of the patient.
 20. A method of providing treatmenttherapy to a volume of neural tissue of a patient comprising the stepsof: (a) implanting a cannula within a predetermined site of the patient;(b) inserting at least two leads into the cannula and directing eachlead outwardly through an opening along a distal end of the cannula,each lead extending from the cannula along a distinct predeterminedtrajectory; and (c) positioning a therapy delivery element on the distalend of each lead to provide treatment therapy to the volume of neuraltissue.
 21. The method of claim 20, wherein the step of implantingcomprises the step of implanting the cannula within a brain of thepatient.
 22. The method of claim 20, wherein the step of implantingcomprises the step of implanting the cannula within a spinal cord of thepatient.
 23. The method of claim 20, wherein the step of implantingcomprises the step of implanting the cannula within a peripheral nerveof the patient.
 24. The method of claim 20, wherein the volume of neuraltissue is selected from the group consisting of a subthalamic neucleus(STN), a peduncular pontine nucleus (PPN), a caudate, a putamen, aninternal palladium, an external palladium, a cingulum, an anterior limbof an internal capsule, an anterior nucleus (AN), a centremedian (CM), adorsal medial nucleus, a nucleus of a thalamus, a hippocampus, astructure in a temporal lobe, a hypothalamus, a structure of adiencephalons, a pons, a medulla, a corext, a cerebellum, a lateralgeniculate body, and a medial geniculate body.
 25. The method of claim20, wherein the therapy delivery element is an electrode.
 26. The methodof claim 25, further comprising the steps of: (d) establishing ananode/cathode relationship between at least two electrodes; and (e)presenting electrical pulses to the established anode/cathoderelationships of the electrodes, whereby neural tissue are activated.27. The method of claim 20, wherein the therapy delivery element is acatheter.
 28. A system for providing treatment therapy to a volume ofneural tissue comprising in combination: (a) cannula having a lumendistal end, the lumen distal end having at least two openings, eachopening capable of directing an object outwardly along a distinctpredetermined trajectory; (b) at least one lead insertable within thecannula and capable of being directed outwardly through one of theopenings of the cannula and having at least one electrode at a distalend of the lead; (c) at least one catheter insertable within the cannulaand capable of being directed outwardly through another one of theopenings of the cannula; (d) a signal generator coupled to the lead forproviding electrical stimulation to the neural tissue; and (e) a drugdelivery device coupled to the catheter for delivering at least one drugto the neural tissue.
 29. The system of claim 28 further comprising: (f)means for selectively adjusting an electric field created by the signalgenerator.
 30. The system of claim 28 further comprising: (f) means forselectively adjusting a rate of drug delivery by the drug deliverydevice to the catheter.
 31. The system of claim 28 further comprising:(f) a sensor for generating a signal related to an extent of a conditionto be treated; and (g) a processor responsive to the sensor foradjusting at least one parameter of a treatment therapy provided by thesignal generator.
 32. The system of claim 28 further comprising: (f) asensor for generating a signal related to an extent of a condition to betreated; and (a) a processor responsive to the sensor for adjusting atleast one parameter of a treatment therapy provided by the drug deliverydevice.
 33. The system of claim 28 further comprising: (a) a sensor forgenerating a signal related to an extent of a condition to be treated;and (b) a processor responsive to the sensor for selectively altering arelative treatment therapy delivery delivered by the signal generator.34. The system of claim 28 further comprising: (a) a sensor forgenerating a signal related to an extent of a condition to be treated;and (b) a processor responsive to the sensor for selectively altering arelative treatment therapy delivery delivered by the drug deliverydevice.
 35. A method for providing treatment therapy to a volume ofneural tissue comprising the steps of: (a) implanting a cannula within abody of a patient; (b) inserting at least one lead into the cannula; (c)directing a lead distal end of first lead outwardly through the cannulaand along a first distinct predetermined trajectory; (d) inserting atleast one catheter into the cannula; and (e) directing a catheter distalend of the catheter outwardly through the cannula and along a seconddistinct predetermined trajectory.
 36. The method of claim 35, furthercomprising the steps of: (f) coupling the lead to a signal generator forproviding electrical stimulation to the neural tissue; and (g) couplingthe catheter to a drug delivery device for delivering at least one drugto the neural tissue.
 37. The method of claim 36, further comprising thestep of: (h) selectively adjusting an electric field created by thesignal generator.
 38. The method of claim 36, further comprising thestep of: (h) selectively adjusting a rate of drug delivery by the drugdelivery device to the catheter.
 39. The method of claim 36, furthercomprising the step of: (h) sensing an extent of a condition to betreated; and (i) adjusting in response to the step of sensing at leastone parameter of a treatment therapy provided by the signal generator.40. The method of claim 36, further comprising the step of: (h) Sensingan extent of a condition to be treated; and (i) adjusting in response tothe step of sensing at least one parameter of a treatment therapyprovided by the drug delivery device.
 41. The method of claim 35,wherein the step of implanting comprises the step of implanting thecannula within a brain of the patient.
 42. The method of claim 35,wherein the step of implanting comprises the step of implanting thecannula within a spinal cord of the patient.
 43. The method of claim 35,wherein the step of implanting comprises the step of implanting thecannula within a peripheral nerve of the patient.
 44. The method ofclaim 35, wherein the volume of neural tissue is selected from the groupconsisting of a subthalamic neucleus (STN), a peduncular pontine nucleus(PPN), a caudate, a putamen, an internal palladium, an externalpalladium, a cingulum, an anterior limb of an internal capsule, ananterior nucleus (AN), a centremedian (CM), a dorsal medial nucleus, anucleus of a thalamus, a hippocampus, a structure in a temporal lobe, ahypothalamus, a structure of a diencephalons, a pons, a medulla, acorext, a cerebellum, a lateral geniculate body, and a medial geniculatebody.
 45. The method of claim 36, further comprising the steps of: (h)establishing an anode/cathode relationship between at least twoelectrodes; and (i) presenting electrical pulses to the establishedanode/cathode relationships of the electrodes, whereby neural tissue areactivated.